Lundgren C H, Brown S L, Nordt T K, Sobel B E, Fujii S
Cardiovascular Division, Washington University School of Medicine, St Louis, MO, USA.
Circulation. 1996 Jan 1;93(1):106-10. doi: 10.1161/01.cir.93.1.106.
Obesity is known to predispose to attenuated fibrinolysis attributable to increased concentrations in plasma of type-1 plasminogen activator inhibitor (PAI-1), the primary physiological inhibitor of endogenous fibrinolysis. PAI-1 is present in neointimal vascular smooth muscle cells and lipid-laden macrophages.
The present study was designed to determine whether PAI-1 expression occurs in adipose tissue as well, thereby potentially contributing to increased cardiovascular risk associated with obesity. 3T3-L1 preadipocytes were differentiated into adipocytes by exposing them to isobutylxanthine (0.5 mmol/L) and dexamethasone (0.25 mumol/L) over 7 days and incubated for 24 hours with transforming growth factor-beta (TGF-beta), known to augment PAI-1 synthesis in several cell types and to be released from platelets when they are activated. TGF-beta increased PAI-1 activity in the conditioned media of the 3T3-L1-derived cells in a concentration-dependent fashion without significantly affecting cell proliferation. Western blotting and immunoprecipitation of 35S-labeled PAI-1 showed that the increased PAI-1 activity paralleled increased PAI-1 protein. Northern blotting showed that increased PAI-1 mRNA preceded increased accumulation of PAI-1 activity and protein in the conditioned media. Furthermore, TGF-beta (10 ng/g body wt) administered in vivo increased PAI-1 activity in mouse plasma and PAI-1 mRNA expression in mouse adipose tissue.
Increased plasma PAI-1 activity in obese human subjects may result from PAI-1 release from an increased mass of adipose tissue, particularly in association with thrombosis and elaboration of TGF-beta from platelet alpha-granules into the circulation. The increased PAI-1 may exacerbate vascular disease by shifting the balance between thrombosis and thrombolysis toward thrombosis and consequently exposing luminal surfaces of vessels to mitogens associated with microthrombi over protracted intervals.
众所周知，肥胖会导致纤维蛋白溶解减弱，这是由于血浆中1型纤溶酶原激活物抑制剂（PAI-1）浓度升高所致，PAI-1是内源性纤维蛋白溶解的主要生理抑制剂。PAI-1存在于血管内膜的血管平滑肌细胞和富含脂质的巨噬细胞中。
本研究旨在确定PAI-1表达是否也发生在脂肪组织中，从而可能导致与肥胖相关的心血管风险增加。通过在7天内将3T3-L1前脂肪细胞暴露于异丁基黄嘌呤（0.5 mmol/L）和地塞米松（0.25 μmol/L）使其分化为脂肪细胞，并与转化生长因子-β（TGF-β）孵育24小时，已知TGF-β可增强多种细胞类型中PAI-1的合成，并在血小板激活时从血小板中释放出来。TGF-β以浓度依赖的方式增加了3T3-L1衍生细胞条件培养基中的PAI-1活性，而对细胞增殖没有显著影响。对35S标记的PAI-1进行蛋白质印迹和免疫沉淀分析表明，PAI-1活性的增加与PAI-1蛋白的增加平行。Northern印迹分析表明，PAI-1 mRNA的增加先于条件培养基中PAI-1活性和蛋白积累的增加。此外，体内给予TGF-β（10 ng/g体重）可增加小鼠血浆中的PAI-1活性和小鼠脂肪组织中的PAI-1 mRNA表达。
肥胖人类受试者血浆PAI-1活性增加可能是由于脂肪组织量增加导致PAI-1释放，特别是与血栓形成以及血小板α颗粒中的TGF-β释放到循环中有关。PAI-1的增加可能会通过将血栓形成和溶栓之间的平衡向血栓形成方向转移，从而使血管腔表面在较长时间内暴露于与微血栓相关的促有丝分裂原，进而加剧血管疾病。
